81 merc 115 inline 6 possible switchbox problem

[loveboating]

Compression all good, fuel system good, spark plugs replaced. However problem started with Tach showing between 5000 and 6000 RPM during actual low RPM reving. Very boggy of the line, fine during higher RPM. Rectifier checks OK. How do I check if Switch boxes are the problem. Also is the Tach going wacky related to the problem. Going on vacation soon need my boat running good, please HELP.

 

[phatmanmike]

Re: 81 merc 115 inline 6 possible switchbox problem

switch boxes have nothing to do with tach. tach gets its feed directly from the rectifier. are you sure its good? replace it with a 3 dollar rectifier from radioshack to double check. very cheap insurance.

is your battery getting charged? check that, if not check the wiring for your tach, they do crap out sumtimes